We investigated the anti-cancer effects of beta-sitosterol (BS), a plant-derived sterol in AGS human gastric adenocarcinoma cells and xenograft mouse models. BS significantly reduced cell viability by inducing apoptosis in AGS adenocarcinoma cells. This was accompanied by the formation of apoptotic bodies, as detected by Annexin V, caspase 3/7 activity, and MitoPotential assay. BS stimulated phosphatase and tensin homolog (PTEN) and phospho-AMP-activated protein kinase (p-AMPK) expression. Pharmacological inhibitors or siRNA were used to further analyse the relationship between the two proteins. AMPK was found to represent a likely upstream regulator of PTEN. Additionally, two-dimensional gel electrophoresis was used to identify related proteins in the treatment of BS. The decrease of Hsp90 protein by BS was observed. Induction of PTEN protein and reduction of Hsp90 was mediated by AICAR, an AMPK activator, indicating that AMPK is necessary for PTEN and Hsp90 expression. Additionally, BS was found to be effective through the regulation of cancer biomarker. Furthermore, BS suppressed tumour growth without toxicity in the AGS xenograft mouse models-. Taken together, the present results demonstrate that BS exerts anti-cancer effects in AGS cells and xenograft mouse models by mediating AMPK, PTEN, and Hsp90.